Null and gain adjustment mechanism and procedure for hydrostatic control systems

ABSTRACT

There is disclosed a control system for interconnecting a plurality of hydrostatic transmissions for synchronous operation. The control system includes means to adjust the null position of the pumps and motors and means to adjust the gain between the two machines.

United States Patent 1 Erickson et a1. Nov. 20, 1973 [54] NULL AND GAINADJUSTMENT 1,751,172 3/1930 Reinhardt 251/78 X MECHANISM AND PROCEDUREFOR 2,274,029 2/1942 Archer 251/285 X 3,158,173 11/1964 Bachli et a1251/78 X HYDROSTATIC CONTROL SYSTEMS 3,477,225 11/1969 Cryder et 60/19[75] Inventors: Rodney R. Erickson, Joliet, 1",; 3,575,378 4/1971 Fawkes1 251/233 w Matthews New Berlin Harter Wis.

[7 3] Assignee: Caterpillar Tractor Co., Peoria, 111. Primary Examinerhwin Cohen 22 Filed; 23 1971 AttorneyFreling E. Baker [21] Appl. No.:211,318

52 US. Cl 91 411, 91/413, 251/233, ABSTRACT 251/234 [51] Int. Cl. Fl5b11/16, Fl5b 13/06 There is disclosed a control system forinterconnecting [58] Field of Search 91/411, 413; 74/469; a plurality ofhydrostatic transmissions for synchro- 251/285, 78, 233, 234; 137/609,637.1 nous operation. The control system includes means to adjust thenull position of the pumps and motors and [56] References Cited means toadjust the gain between the two machines.

UNITED STATES PATENTS 971,764 10/1910 Lutz 74/522 4 Claims, 3 DrawingFigures PATENIEnnnv 20 um 3.772.964

' SHEET 10? 2 I NVEN TORS RODNEY R. EPJCK'SON RALPH w. MAJ-thaws fw 7-WM ATTORNEYS PATENTEuuuvzo' ma 3,772,964

sum 2 BF 2 INVENTORS RODNEY RRLPACRfiON MPH \N-MATTHEVVS ATTORNEYS BYwgw w w +4 NULL AND GAIN ADJUSTMENT MECHANISM AND PROCEDURE FORHYDROSTATIC CONTROL SYSTEMS BACKGROUND OF THE INVENTION This inventionrelates to control means and pertains more particularly to control meansfor synchronizing the output of a plurality of hydrostatictransmissions.

Hydrostatic transmissions are now being employed in heavy duty vehicleswherein steering is accomplished by differential drive of the wheels byseparate hydrostatic drive transmissions. Such a drive system isdisclosed in U.S. Pat. No. 3,477,225 issued Nov. 11, 1969 to IR. Cryder,et al., and assigned to the assignee of the present invention.

Hydrostatic transmissions normally employ a hydraulic pump supplyingpressurized fluid to a hydraulic motor connected to supply torque to thedrive wheels. Either the pump, the motor, or both may be variable.

When hydrostatic transmissions are used in vehicles such as track layingvehicles and two wheeled tractors, steering is normally accomplished byvarying the drive to each side of the vehicle rather than braking eitherside as in previously known systems. Such systems normally employseparate hydraulic motors for each side of the vehicle. These motors maybe supplied by a single pump or from separate pumps. In either case,either the motors or the pump must be variable in order to effectsteering.

One problem with such systems having either one or two pumps, and twomotors is in providing a control system having provision for precisesynchronism between the drive motors. The need for synchronism isespecially critical when the steering control is in the neutral positionfor movement of the vehicle in a straight line. Without preciseadjustments or position correspondence of the pump and/or motors, thevehicle will not travel in a straight line.

SUMMARY OF THE INVENTION It is the primary object of the presentinvention to provide control means for adjusting the null and gaincharacteristics of a hydrostatic control system.

Another object of the present invention is to provide control means forinterconnecting a plurality of hydraulic machines for positioncorrespondence.

A furtherobject of the present invention is to provide I control meansfor adjustably interconnecting the servo BRIEF DESCRIPTION OF THEDRAWINGS The above and other objects and advantages of the presentinvention will become apparent from the following description when readin conjunction with the accompanying drawings wherein:

FIG. 1 is a diagrammatic illustration of a preferred embodiment of thepresent invention;

FIG. 2 is a detailed illustration of a portion of the embodiment of FIG.1; and,

FIG. 3 is an elevational view of a pivotal support bracket for thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to thedrawings, and in particular to FIG. 1, there is schematicallyillustrated a pair of variable displacement hydraulic machines 10 and 12which may be either pumps or motors. These machines 10 and 12 may beconstructed such as those shown in U.S. Pat. Nos. 3,381,472 issued May7, 1968 to C. Brown, et al. or U.S. Pat. No. 3,477,225 issued Nov. 11,1969 to JR. Cryder, et al. In the presently contemplated embodiment, themachines may be preferably an identical pair of hydraulic motors forminga part of a hydrostatic transmission system and each separately driving,for example, the separate track of a crawler vehicle.

The machines 10 and 12 are interconnected to operate together to providespeed control, both together and independently to provide straight linetranslation of the machine, and also to provide turning ability. Thevariable displacement of each of the machines is controlled be a servovalve. Each of the hydraulic machines 10 and 12 is provided with controlmeans for adjusting the null or zero displacement of the servo valvemechanism. This adjusting mechanism is identical with respect to bothmachines and will be shown generally at 14 only with respect to themachine 12. It is to be understood thateach pump and motor will havesuch a mechanism.

The servo control mechanism comprises, for example, a servo valve 16,mounted such as by a bracket 18 into the pump or motor housing.

The servo valve 16 is operatively connected to a control lever or arm 20by means of an arm 22 and a bracket 24 having a pair of adjusting screws26 and 28 for adjusting the servo valve with respect to the control arm20. The spring 30 biases the arm 22 into engagement with the adjustingscrew 26.

The relative position of the servo valve 16 may be adjusted with respectto the control lever 20in order to provide a corresponding null or zeroposition. The adjustment may be accomplished by setting the control arm20in its preferred zero position and adjusting the servo valve 16 bymeansof adjusting screws 26 and 28 such that the servo valve is then ina corresponding zero position. This procedure positions the servo valvewithin its cooperating servo sleeve or housing to a position thatsignals or actuates the pump or motor to a null displacement position. l

The two machines 10 and 12 are interconnected by control means whichprovides for a sensitivity or gain adjustment of the two pump servovalves to control the synchronization between the two machines. Each ofthe machines is provided with a sensitivity or gain adjustment mechanismgenerally designated by the numeral 32. These are identical inconstruction and thus, only one will be described in detail withreference nu merals applied to both.

The gain or sensitivity adjustment mechanism generally conprises asteering cylinder or motor 34 carried by a supporting bracket 36 whichin turn is pivotally mounted such as by means of a pin 38 from a fixedportion of the machine. The pivotally mounted bracket 36 and cylinder 34together act as a lever or bellcrank for operatively connecting a speedcontrol motor 40 to the control lever 20 by means of a rod or link 42.The rod or link 42 is pivotally connected to the bracket 36 by means ofa pin 44 slidably disposed in a slot 46 of the bracket. The lever armformed between pivots 38 and pin 44 is adjustable by means of anadjusting screw 48 carried on the bracket 36. The pin 44 is moved alongthe arcuate slot 46 by means of a yoke 50 which is operatively connectedto a piston 52 of the steering motor 34. The piston 52 is biased to aretracted position by means of a spring 54 disposed between shoulders 56fixed to the motor housing, and shoulder 58 carried by the piston. Thisretracted position of the piston 52 also positions the pin 44 by meansof yoke 50 against the adjusting screw 48 to maintain a preselectedlever arm and eliminates slop or slack in the linkage due to wear and/orclearance.

A tie rod 60 operatively couples the two gain adjustment mechanisms 32for simultaneous movement of the two interconnected servo valves bymeans of the speed control motor 40. The sensitivity or gain adjustmentmechanisms are separately adjustable so that they may be synchronizedfor position correspondence. That is, so that both motors or pumps willbe operated at the same R.P.M. or the same output so that the vehiclemay maintain a straight line heading for various speed settings of theseparate transmissions.

Steering is accomplished by changing the displacement of one of themachines with respect to the other. This change of displacement isaccomplished by actuation of one of the pumps or motors 34 whilemaintaining the other motor and the speed control motor 40 at a constantadjustment. Pressurization of the steering motor is accomplished byintroduction of hydraulic fluid into the chamber 62 for acting on piston52, and movement of the piston in the cylinder moves the yoke 50 withrespect to the bracket 36 carrying the pin 44 along arcuate slot 46. Themovement of pin 44 along the arcuate slot 46 cams the pin 44 formovement of the rod 42 one way or the other and consequently, movementof the control lever 20.

The movement of the control lever 20 acts to reposition the servocontrol valve 16 and thus repositions the displacement control mechanismof the hydraulic machine 12. This action will cause the hydraulicmachine 12, if it is a motor, for example, to speed up or slow down withrespect to the machine 10. This results in a turn of the vehicle. On theother hand, considering the machine and 12 to be pumps, this adjustmentwould increase or decrease the flow of one pump with respect to theother, resulting in an increase or decrease in output from that pump andconsequently, an increase or decrease in the motor driven thereby.Hydraulic fluid is introduced into the chamber 62 by way ofa conduit 64formed in the bracket 64 and communicating therewith, and with conduit66 in pin 38.

From the above description it can be seen that there is disclosed acontrol mechanism for interconnecting a plurality of hydrostatictransmissions and including means for adjusting and synchronizing thetwo transmissions.

While the present invention has been described with respect to aspecific embodiment, it is to be understood that many changes andmodifications may be made in the illustrated construction withoutdeparting from the spirit and scope of the present invention as definedin the appended claims.

We claim:

1. The combination of adjustable control means interconnecting a controlelement of a plurality of variable displacement hydraulic machines, saidcombination comprising:

a plurality of variable displacement hydraulic machines;

a servo control valve and actuating means disposed in each of saidmachines for controlling the displacement thereof;

a first pivotal control lever means for actuating the control valveactuating means of each of said machines;

means for adjustably connecting each of said control valve actuatingmeans to each of said levers so that the null position of said valve canbe adjusted with respect to said lever;

means including a pivotally mounted bellcrank connected to each controllever, each bellcrank including a slot means, a link member connectingeach bellcrank to its respective control lever, said link memberincluding a pin movable within said slot means, adjustment means forasjusting the position of said pin within said slot means;

a tie rod means interconnecting said bellcranks;

first hydraulic means operatively interconnected with all saidbellcranks to simultaneously actuate said control valves; and,

second hydraulic means connected to each said pin for selectivelyactuating one of said control valves with respect to the other of saidcontrol valves.

2. The combination of claim 1 wherein said second hydraulic meanscomprises a hydraulic ram carried by each of said bellcranks andincludes yoke means connecting said ram to said pin to move said pinalong said slot means.

3. The combination of claim 2 wherein said slot means intersects thepivot axis of said bellcrank and extends to both sides thereof;

said first hydraulic means is connected to said tie rod means.

4. The combination of claim 3 wherein said adjustment means is disposedat one end of said slot means to engage and position said pin withrespect to said one end of said slot means; and

spring means operatively connected to bias said pin toward saidadjustment means. a:

1. The combination of adjustable control means interconnecting a controlelement of a plurality of variable displacement hydraulic machines, saidcombination comprising: a plurality of variable displacement hydraulicmachines; a servo control valve and actuating means disposed in each ofsaid machines for controlling the displacement thereof; a first pivotalcontrol lever means for actuating the control valve actuating means ofeach of said machines; means for adjustably connecting each of saidcontrol valve actuating means to each of said levers so that the nullposition of said valve can be adjusted with respect to said lever; meansincluding a pivotally mounted bellcrank connected to each control lever,each bellcrank including a slot means, a link member connecting eachbellcrank to its respective control lever, said link member including apin movable within said slot means, adjustment means for asjusting theposition of said pin within said slot means; a tie rod meansinterconnecting said bellcranks; first hydraulic means operativelyinterconnected with all said bellcranks to simultaneously Actuate saidcontrol valves; and, second hydraulic means connected to each said pinfor selectively actuating one of said control valves with respect to theother of said control valves.
 2. The combination of claim 1 wherein saidsecond hydraulic means comprises a hydraulic ram carried by each of saidbellcranks and includes yoke means connecting said ram to said pin tomove said pin along said slot means.
 3. The combination of claim 2wherein said slot means intersects the pivot axis of said bellcrank andextends to both sides thereof; said first hydraulic means is connectedto said tie rod means.
 4. The combination of claim 3 wherein saidadjustment means is disposed at one end of said slot means to engage andposition said pin with respect to said one end of said slot means; andspring means operatively connected to bias said pin toward saidadjustment means.